In communications and electronic engineering, antennas are used for the conversion between electrical power and radio waves. During transmission, a radio transmitter may supply an oscillating radio frequency electric current to an antenna's terminals to cause the antenna to radiate the energy as electromagnetic waves. During reception, an antenna may intercept some of the power of electromagnetic waves in order to produce a small voltage at the terminals of the antenna. The small voltage is applied to a receiver to be amplified. Antennas may be used in systems such as radio broadcasting, broadcast television, two-way radio, communications receivers, radar, cell phones, and satellite communications, as well as other devices such as garage door openers, wireless microphones, Bluetooth devices, and wireless computer networks, etc. Antennas exist in different sizes and models depending on the purpose of the antenna.